Field of the Invention:
The invention lies in the automotive technology field. More specifically, the invention relates to a device for sensing an object or a person in the interior of a vehicle. The device is of the type including a laser for emitting laser pulses and an optical receiver for receiving laser pulses which are reflected or diffracted at an object or at a person.
Persons who are displaced far forward in the direction of the dashboardxe2x80x94such as children in so-called rearward facing baby seats on the front-seat passenger seatxe2x80x94are subjected to the hazard, during the operation of a motor vehicle provided with an airbag, of suffering injuries as result of the inflation impact of the airbag in the event of an accident. Modern control systems for personal protection aim at switching off the airbag in such situations or inflating it with reduced force and speed in order to avoid the risk of injury to a vehicle occupant. In order to determine the position of the vehicle occupant in the vehicle, use is preferably made of contactless, optical sensors. European published patent application No. 0 669 227 A1 discloses a device for the contactless detection of an object or of a person in the interior of a vehicle. There, the vehicle seat is irradiated by a number of LEDs. The beams which are reflected from the seat or a person or an object on the vehicle seat are registered by a photodetector field.
The light source used for the optical detection system is preferably a laser which permits positionally precise sensing owing to its monochrome radiation. Laser diodes, and in particular semiconductor laser diodes, are usually used as transmitters.
In order to avoid continuous loading of persons in the interior of the vehicle with energy from the laser, the laser is operated in a pulsed fashion. However, even in this mode of operation, the health of the vehicle occupant must not be adversely affected by the emitted laser pulses in any way.
Furthermore, the known device has the disadvantage that the optical receiver receives a reflected laser pulse with a very high energy content if an object is disposed in very close vicinity to the laser and the transmission pulse has a high energy content. Owing to the short distance between the optical detection apparatus and the object, only a small amount of the emitted energy is lost. This effect is amplified if the object has a highly reflective effect. Given such a large absorption of energy by the optical receiver, there is the hazard that the amplifier which is connected downstream may be operated in the saturation region, and precise detection of the object or of the distance between the object and the optical detection apparatus may thus no longer be possible.
It is accordingly an object of the invention to provide a device and a method for detecting animate or inanimate objects in the vehicle interior, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which is improved and further developed in such a way that any hazard to persons in the interior owing to the emitted laser radiation can be prevented at any time, and at the same time correct detection data are made available.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for sensing an object (inanimate object or person) in the interior of a vehicle, comprising:
a laser for emitting laser pulses;
an optical receiver for receiving laser pulses reflected or scattered at an object in an interior of a vehicle;
a control apparatus connected to the laser and to the optical receiver for setting an energy content of a following laser pulse as a function of a characteristic variable of a registered or reflected laser pulse.
In accordance with an added feature of the invention, the control apparatus sets a transmission power of the laser.
In accordance with an additional feature of the invention, the control apparatus sets a pulse length of the laser pulse.
In accordance with yet an additional feature of the invention, the control apparatus sets a pulse length for a predefined laser power and sets a laser power differently from the predefined laser power as soon as a pulse length drops below a predefined limiting value.
In accordance with another feature of the invention, the control apparatus reduces the energy content of the following laser pulse based on a current energy content thereof if the characteristic variable of the reflected laser pulse exceeds an assigned sensitivity limiting value.
In accordance with a further feature of the invention, the control apparatus increases the energy content of the following laser pulse based on a current energy content thereof if the characteristic variable of the reflected laser pulse drops below an assigned sensitivity limiting value.
In accordance with again an added feature of the invention, the control apparatus increases the energy content of the following laser pulse only up to an assigned hazard limiting value.
In accordance with again an additional feature of the invention, the optical receiver includes a plurality of receiver elements connected to interact with the laser, and wherein the control apparatus is adapted to increase or decrease the energy content of the following laser pulse based on the current energy content thereof if the characteristic variable of at least one of the reflected laser pulses registered by the receiver elements drops below or exceeds an assigned limiting value.
In accordance with a concomitant feature of the invention, the characteristic variable is defined as a strength or a power or an energy content of the reflected laser pulse.
With the above and other objects in view there is also provided in accordance with the invention, a method for sensing an object in an interior of a vehicle, and particularly a method for operating the above-outlined device.
The method comprises:
emitting a laser pulse;
registering the reflected laser pulse after reflection at an object; and
determining an energy content of a following laser pulse to be emitted from a characteristic variable of the reflected laser pulse.
In this context, a control apparatus is provided which sets the energy content of a laser pulse as a function of a characteristic variable which is acquired by evaluating a reflected laser pulse. Here, the reflected laser pulse which is received directly before the recent emission of the laser pulse is preferably evaluated. The energy which is output by the laser is thus reduced at all times to an amount which is, on the one hand, sufficient to detect an object or a person to an adequately defined degree, but on the other hand avoids any hazard to vehicle occupants. The device is thus operated in an optimized way in terms of its detection sensitivity and its radiation loading.
The energy content of an emitted laser pulse is determined via the product of the transmission power and pulse length. The control apparatus which is preferably designed as a microprocessor or else as a circuit with discrete components preferably adjusts either the transmission power of the laser or the pulse length. The transmission power is preferably set by means of an operating current of the laser.
Characteristic variables of a registered, reflected laser pulse are, in particular, its strength/amplitude or its power or its energy content. In such a case, the optical receiver is usually a converter which converts optical signals into electrical signals. Consequently, the control apparatus preferably registers an electrical signal which is supplied by such an optical receiver, and evaluates one or more of the characteristic variables described above.
An advantageous control specification is explained below with reference to the evaluation of the energy content of a registered, reflected laser pulse. The energy content of the reflected laser pulse is determined by the product of the power and pulse length. The control specification provides that, in the event of the energy content of the reflected laser pulse being above a sensitivity limiting valuexe2x80x94which characterizes the energy content of a reflected laser pulse which is just sufficient to detect an object or a personxe2x80x94, the energy content of the following transmit-end laser pulse is reduced starting from its previous, current energy content. The evaluation-of the reflected laser pulse has shown that the device is operated with a laser power which is too high to sense an object or a person. The laser power is therefore reduced. In this context, the device may be designed as an adjustment device which adjusts the energy content of the reflected laser pulse as a regulating variable to the predefined sensitivity limiting value as a setpoint value.
If, on the other hand, a reflected laser pulse is received with an extremely low energy content, according to the invention the laser power is increased, at least until the sensitivity limiting value can be sensed as energy content at the receive end.
The energy content of a reflected laser pulse in such a device is determined essentially by the distance between an object at which the emitted laser pulse is reflected, and the optical receiver and in particular by the diffraction properties of the irradiated object or the irradiated person. The further the object is away, the smaller the energy content of the reflected laser pulse. The brighter the surface of the object, the better the diffraction properties which it has. In one advantageous development of the invention, the control apparatus determines the energy content or the power or the amplitude of the reflected laser pulse in order to be able to detect the distance and thus the position of the object or of the vehicle occupant. On the basis of these properties of the device, the transmission power will be regularly adapted if the distance between an object or a person and the sensing device changes significantly.
The risk that the transmit power of the laser is set at increasingly high levels, and thus of instability of the adjustment owing to the fact that there are no reflected laser pulses, or weakly received reflected laser pulses during the emission of a laser pulse xe2x80x9cinto the voidxe2x80x9d is countered by the arrangement of the device: owing to the function of the device, the laser will sense either a vehicle seat or the hazard area in front of an airbag. Even if an object or a vehicle occupant is not present, the laser will always be directed onto a permanently installed vehicle structure which is at a maximum distance of approximately one meter from the sensing device. If the laser is intended to sense the hazard area in front of an airbag, and is therefore arranged in the roof lining, a laser pulse which is emitted is at least reflected by the footwell of the vehicle. In one advantageous development of the invention, the problem of unstable adjustment is additionally solved by virtue of the fact that the energy content of an emitted laser pulse is limited to a hazard limiting value. This provides a means of preventing high-energy laser power, which thus presents a hazard to vehicle occupants, from being emitted, in addition to the fact that the sensing apparatus is, as described above, arranged opposite a vehicle structure.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for sensing an object or a person in the interior of a vehicle, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.